In a plasma processing chamber, such as a plasma etch or plasma deposition chamber, the temperature of a chamber component is often an important parameter to control during a process. For example, a temperature of a substrate holder, commonly called a chuck or pedestal, may be controlled to heat/cool a workpiece to various controlled temperatures during the process recipe (e.g., to control an etch rate). Similarly, a temperature of a showerhead/upper electrode or other component may also be controlled during the process recipe to influence the processing. Conventionally, a heat sink and/or heat source is coupled to the processing chamber to maintain the temperature of a chamber component at a desired temperature. Often, at least one heat transfer fluid loop thermally coupled to the chamber component is utilized to provide heating and/or cooling power.
While most systems typically run the heat transfer fluid loop at a fixed flow rate with the heat transfer fluid reservoir at a fixed temperature, the above referenced related applications teach the advantages of modulating the heat transfer liquid flow rate based on a temperature control algorithm to achieve better temperature control (improved responsivity, less overshoot, etc.). These related applications also describe digital valves with pulse wave modulation (PWM) to change a duty cycle of a heat transfer liquid for control of a temperature. While economical, digital valve architectures may however be subject to frequent actuation and correspondingly limited lifetimes. Also, depending on liquid mass flow rates in the heating and cooling loops, abrupt valve closures may impart large momentum changes (i.e., fluid hammer) causing pressure waves increasing the risk of mechanical failures in the system.